Change the font in the Sequencer Text Effect with Python code
First, you' have to know where the font-files are located in your system. You can find this location by changing manually a font. On my Windows machine, this is: C:\WINDOWS\Fonts\ARIAL.TTF for the Arial font. Then paste and run run the followig code in the Text Editor of the Scripting workspace to assign the Arial font to the active (selected) strip.
import bpy
strip  = bpy.context.scene.sequence_editor.active_strip
new_font = 'C:\WINDOWS\Fonts\ARIAL.TTF'
strip.font = bpy.data.fonts.load(new_font) 

See also Select text object by name and change font via script